Voltammetric determination of isoxsuprine and fenoterol in dosage forms and biological fluids through nitrosation

A simple and highly sensitive voltammetric method was developed for the det ermination of isoxsuprine HCI (I) and fenoterol HBr (II) in dosage forms an d biological fluids. The method is based on treatment of the two compounds with nitrous acid followed by measuring the cathodic current produced by th e resulting nitroso derivatives. The voltammetric behavior was studied adop ting Direct Current (DCt), Differential Pulse (DPP) and Alternating Current (AC(t)) polarography. Both compounds produced well-defined, diffusion-cont rolled cathodic waves over the whole pH range in Britton-Robinson buffers ( BRb). At pH 11 and pH 9, the values of diffusion-current constants (Id), we re 9.4 +/- 0.3 and 7.7 +/- 0.4 For I and II, respectively. The current-conc entration plots for I were rectilinear over the range of 0.6-12 mug/ml and 0. 1- 12 mug/ml in the DCt and DPP modes, respectively. As for II, the rang e was 1-20 mug/ml and 0.1-20 mug/ml in the DCt and DPP modes, respectively. The minimum detectability (S/N=2) were 0.02 mug/ml (approximate to 6 x 10( -8) M) and 0.01 mug/ml( approximate to 2.6 x 10(-8) M) for I and II, respec tively, adopting the DPP mode. The proposed method was applied to the deter mination of both compounds in dosage forms and the results obtained were in good agreement with those obtained using reference methods. The proposed m ethod was further applied to the determination of isoxsuprine in spiked hum an urine and plasma. The percentage recoveries adopting the DPP mode were 9 8.84 +/- 1.18 and 99.36 +/- 0.97, respectively. (C) 2000 Elsevier Science B .V. All rights reserved.